text: Capillary electrochromatography (CEC) combines the principles used in HPLC and CE. The mobile phase is driven across the chromatographic bed using electroosmosis instead of pressure (as in HPLC). Electroosmosis is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane or any other fluid conduit. Electroosmotic flow is caused by the Coulomb force induced by an electric field on net mobile electric charge in a solution. Under alkaline conditions, the surface silanol groups of the fused silica will become ionised leading to a negatively charged surface. This surface will have a layer of positively charged ions in close proximity which are relatively immobilised. This layer of ions is called the Stern layer. The thickness of the double layer is given by the formula:
  where ε is the relative permittivity of the medium, ε is the permittivity of vacuum, R is the universal gas constant, T is the absolute temperature, c is the molar concentration, and F is the Faraday constant
  When an electric field is applied to the fluid (usually via electrodes placed at inlets and outlets), the net charge in the electrical double layer is induced to move by the resulting Coulomb force. The resulting flow is termed electroosmotic flow. In CEC positive ions of the electrolyte added along with the analyte accumulate in the electrical double layer of the particles of the column packing on application of an electric field they move towards the cathode and drag the liquid mobile phase with them.
  The relationship between the linear velocity u of the liquid in the capillary and the applied electric field is given by the Smoluchowski equation as 
  where ζ is the potential across the Stern layer (zeta potential), E is the electric field strength, and η is the viscosity of the solvent.
  Separation of components in CEC is based on interactions between the stationary phase and differential electrophoretic migration of solutes.